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Rivers and Lakes
The seventh episode of Mesozoic Earth. It focuses on life in the rivers and lakes. Animals featured *''Arganodus'' *''Siderops'' *''Freshwater Ichthyosaur'' *''Delphinichthys'' *Cichlid *''Freshwater Mosasaurus'' *Kakanaut Leatherback *''Eudimorphodon'' *''Dallasaurus'' *''Pannoniasaurus'' *Bakonydraco *''Coelophysis'' *''Siamosaurus'' Plot Sequence One The river system of the Chinle Desert in New Mexico, is strong. The water here is fresh. And home to an abundance of a metre long lungfish, called Arganodus, or the Chinlean Lungfish. They feed on the crustaceans that thrive here, including the burrowing crayfish. But every year, this area suffers an intense drought. The rivers turn into a puddle stream system. The fish here will bake in the sun and die. But the Giant Lungfish have a special adaptation. The water is turning anoxic, low in oxygen, the Arganodus can breathe air, because in addition to gills, they also have lungs. But sometimes, conditions get too bad, and the rivers dry up completely. To survive this, the lungfish cocoon and burry themselves in the ground, a form of aestivation, and will remain there until the rains come. But during this time, they are completely defenseless. A subadult Postosuchus enters the river. The ground is very hot, and baked dry. The ground actually crusts. The Postosuchus has a superb sense of smell, and can smell the fish hibernating under the ground. He digs one out and pulls it out, while the cocoon is still on. He then breaks the cocoon open and feeds on the lungfish. Water is in the cocoon as well, and so the Postosuchus drinks. After ten months of severe drought, clouds gather. A monsoon begins. The massive amount of water dumped on the landscape fills the rivers back up to their once great sizes. Rain is the source of all fresh water on this planet. For the lungfish that have survived, they emerge from the burrows, and continue their lives. Sequence Two Sequence Three Sequence Four Lake Erebet, in the northernmost tip of Canada. A massive blizzard sweeps across the icy surface. The lake is covered in three metres of ice. Because of this, very, very few reptiles, or mammals live here. It is winter. It is the Berriasian, the very start of the Cretaceous. The Earth, is cooling down. As it did, polar regions locked up some water. While there are no true permanent glaciers (except in the mountains), lakes have formed from the retreating water. And Lake Erebet is one of them. Beneath, the ice has gripped tight, crushing coral like animals. Here, live the world's only freshwater starfish. But they are better known for their great number of cichlids. Cichlids of all types live here. During the day, they are amazing, in the great circus they make. But at night, things get very scary indeed. The cichlids fall asleep, or hide in the ice, or rocks. There are ice caves here, and they hold the only population, of Delphinichthys erebeticus; electric dolphinfish, who resemble Cornish Jacks. Like cornish jacks, they detect prey using an electric field. But they are strong enough to zap and kill a cichlid. They are huge, at two metres long. They are the top predators here. The scariest part, is that they hunt in cooperative packs. They use their electric fields to communicate with one another as well. They are very fast, and there is no chance of a cichlid escaping once it has been detected. They scour the rocks and ice. Suddenly, from the coral-like structures, a dolphinfish lunges into a crevices to catch a cichlid. Soon, five other dolphinfish gather in a ferocious feeding frenzy. When they find food, they will turn from cooperative hunters, to savage killers, forming intense feeding frenzies. Then, it calms. The dolphinfish continue to scour. The starfish is not a prey item. It has toxins that are fatal to any fish, allowing them to thrive uncontrollably. The dolphinfish are also endothermic, making them warm-blooded. Suddenly, another dolphinfish dives into an ice crack and a feeding frenzy attracts twenty fish to join in the dangerous feast. It calms yet again. Some prefer to attack cichlids who wander out, so that they don't get injured in the feeding frenzies. But the main gang is on the move, forty of them, looking, for hiding cichlids. And using their electrical organs, they detect an entire shoal inside a rock crevices. The biggest feeding frenzy is about to erupt. Suddenly, one lunges and all forty dive and all turn heartless. The water echoes with the sound of electrical shocks. The very lucky cichlids who escape are caught by the wandering dolphinfish. This happens, all night. Dolphinfish, are highly intelligent, in fact, probably the most intelligent fish. The sun rises. The rays that do enter the ice, provide little light for the lake animals below. The dolphinfish return to the ice cave. There, they have their own residence, and will "sleep". The cichlids return. Paradise, again, until tonight. Sequence Five Some other lakes freeze over during winter, like Lake Poteryali, in Siberia. In it, are absolute beauties. Leatherback sea turtles dive here, but they are very, very fast, and highly unusual. They are warm-blooded. A pack are attacking a shoal of fish, with dead on accuracy. The lake also contains the worlds only truly freshwater mosasaur; Mosasaurus beaugei poteryalii. One swims off. They mainly prey on fish, and are very calm, and the least aggressive mosasaurs of them all, and have no natural predators. This lake is massive, and was created only a few thousand years ago, when the Arctic Ocean above retreated. A population of saltwater Mosasaurus were trapped, and over time, adapted to the harsh conditions, in this weird lake. Sequence Six Sequence Seven We are at the forests of Texas. Clouds gather. This area gets hit with severe storms. The thunder claps in the air. Then, it rains. Each drop of water is the size of a fingernail, and can actually damage leaves it is so hard. This creates various pot holes in the landscape. Then, the winds come, and the rain goes sideways. The river here has it's waters blow out of it and across the land. The river is separate from the forests. The rains flood the landscape, and the river becomes three times as wide then it was before. A week later, in the red canyon, rainwater flows, forming a massive river. The water goes off the edge, forming a massive waterfall. The waterfall will stay here for a few months. The waterfall supplies the wide river, and now streams of water branch off from the river, and a delta system is born. For the animals that live here, it is a relief. And for some, an opportunity. Small teleost fish are falling from the waterfall, and into the river. They make this annual migration every year to reproduce. It is only when the rain waters connect to the canyon and form the waterfall, that they can come. As they swim into the river, some animals take notice. Sitting on the bank of the river, is a Dallasaurus, a tiny monitor lizard, only half a metre long. Others sit on the banks as well. They spot the fish, and they plop into the water. The fishes are not prepared. Suddenly, the Dallasaurus flick their tails and catch the fish, who now race on. Once they catch the fish, they exit half their body out of the water, eat the fish whole, then dive down again, and repeat the process. The fish suffer heavy losses, but the shoal is 7,000 strong, and they are not repelled by this. By the time they pass, 97% of them, have survived. Dallasaurus are in fact, very basal mosasaurs, aquatic monitor lizards. They use these rivers to catch the fish, and to attract a mate. One male is swimming, flicking his forked tongue, to locate a female. He spots one and she is scared. There is a reason. She gets out of the water, but the male leaps out and bites her neck hard, slamming her onto the ground. He vigorously mates with her, and then she doves back into the water and swims off. Males are aggressive towards females, but it is unknown why. The Dallasaurus eventually have to leave themselves. They go off one river, and it leads them back to the ocean. The waterfall becomes weak, and so does the canyon river. A sandstorm hits the desert plains. It does not bode well with the river. But the clouds gather again. This time, it rains harder than it ever has before. The entire landscape becomes flooded. This is the biggest flood in the Cretaceous world. The water follows into the small valley's creating temporary waterfalls. Any animal within it's range, will be drowned, smothered, and killed. This is the most extreme example, of seasonal changes, in the world. Sequence Eight It is the wet season, and in the rivers of Hungary, an animal is making an annual migration. An adult female Pannoniasaurus takes a deep breath, then dives back down. She is a basal mosasaur, and is pregnant. She gets into position, to give birth, to live young. She pushes, and it takes ten seconds to give birth to eight pups. But the pups must leave the waters. They find a branch from a tree low, above the surface. One pup finds it and climbs up. The pups look like monitor lizards, which they are. They have to stay safe in the trees, and in the water, is a good reason why. One pup isn't able to find a branch. Then, a Bakonydraco swoops down, and plucks it from the waters. She lands on the shore to feed on the pup. Another pup finds a branch. Suddenly, an adult Pannoniasaurus rushes to him. He climbs up the branch. Then, the adult leaps out of the water and snatches the baby. The young live in the trees, to avoid their cannibalistic parents. Up here, is plenty of food for them. Some berries grow, and already, a pup is feeding on them. They will spend the next two years in these trees. The Pannoniasaurus finishes up eating berries, and spots a dragonfly. He leaps, and catches it, then eats it. These trees provide rich food for them, but these rivers are highly seasonal, and the wet world can turn into a dry bakery in a blink of an eye. It is now the dry season, and the river is a muddy puddle. The adult Pannoniasaurus have to leave. The trees here are dying, and the berries, no longer in evidence. The young Pannoniasaurus stay here to avoid the hot sun, and there are still insects available for them. Many young will die in this hot world. But it doesn't last forever, fortunately. The clouds gather, and it rains, causing widespread flooding. Soon, the rivers are back at full strength, and the trees are holding berries again. Four years later, one of the pannoniasaur pups is fully grown, and swimming in the river, looking for food. He is now fully adapted to life in these waters. His tail has the very slight beginnings of a tail fluke. His flippers are like a manatees, with small toenails, the last remnants of claws. In the future, all mosasaurs will have tail flukes and no claws. He goes to some bushes growing on the rivers edge. During the wet season, bright red berries grow heavily. He approaches the bushes and feeds on the berries. After he feeds on a few, plucking them delicately, he dives back down. Fish are also on his diet. As the dry season arrives, he leaves the river. He goes to another river. He has caught a fish and eats it. Then, he finds the same berries here and feeds on them too. Early mosasaurs like Pannoniasaurus are seed dispersers, and so in the rivers and lakes of Europe, these berries are found wherever Pannoniasaurus is. In the future, some mosasaurs will feed on seaweed. Sequence Nine